Hitherto, in working one workpiece in multilevel, a machine tool which includes front and back main spindles respectively having axis lines parallel with each other and front and back working tools is used and the workpiece is passed sequentially between the spindles. Still further, there is known a machine tool which includes pluralities of front and back working tools and switches the tools only by controlling the machine tool. Thereby, the machine tool permits to decrease frequency of replacing the tools even if work types are frequently changed and to deal with small lot production of many products in a shorter time.
For example, as shown in FIG. 11, there is known a machine tool 500 which includes a front spindle 510 disposed on a front headstock 511 and movable in an axis-line direction (Z-axis direction), a back spindle 520 having an axis line in parallel with that of the front spindle 510, disposed on a back headstock 521 and movable in the Z-axis direction as well as a direction orthogonal to the Z-axis direction (X-axis direction), and front and back tool posts 541 and 531 having a plurality of front working tools 540 and back working tools 530, respectively, wherein the front tool post 541 is configured to be movable in the Z- and X-axis directions.
The machine tool 500 is configured so that the back tool post 531 is movable in the X-axis direction as well as a direction orthogonal to the Z- and X-axis directions (Y-axis direction). The machine tool 500 sequentially works front and back sides of a workpiece while passing the workpiece between the spindles (see Patent Literature 1, for example).